This invention relates to multi-section sleeves which are readily mountable onto and dismountable from cylinders, and to methods for mounting and dismounting these multi-section sleeves.
One prior art segment in which sleeves are mounting onto and dismounted from cylinders is in flexographic printing. In early printing operations, flexible printing plates were mounted onto the outer surface of a plate cylinder. These plates were used for printing of ink images onto a printing medium. Typically, the back of the plates was adhered directly to the plate cylinder. Since these plates were not readily interchangeable from one cylinder to another, the use of a multiplicity of plate cylinders to perform a multiplicity of jobs were required. This presented severe storage and cost problems to the end user.
Therefore, in an effort to overcome this problem, unitary printing sleeves were developed which were mountable onto and dismountable from the plate cylinders. Compressed gas, generally compressed air, passing in a substantially radial direction from holes located within the plate cylinders, was used to expand the unitary sleeve to a limited extent for facilitating the mounting and dismounting operations.
The first patent to describe this mode of mounting and dismounting of a printing sleeve was described in U.S. Pat. No. 3,146,709. In that patent, a "wound" unitary sleeve, i.e., a helically wound paper sleeve, was fitted onto a hollow cylinder. The sleeve was used as a carrier roll for rubber printing plates attached thereto. Air pressure was radially applied through the holes in the external surface of the cylinder for limited expansion of the sleeve. The sleeve was then axially mounted onto the cylinder by moving the cylinder to an upright position and filling the internal chamber of the cylinder with compressed air. As the sleeve was moved over the upper end of the cylinder, the exiting air expanded the sleeve and a lubricating air film was interposed between the inner sleeve and the outer cylinder. This air film permitted the axial movement of the sleeve to a position about the cylinder. When the sleeve was in such a position, the air flow was terminated, and the sleeve contracted in place about the cylinder. One problem with this sleeve is that today's quality requirements mandate surface tolerances which cannot be maintained by this sleeve. Also, these sleeves are very fragile and printers can't cut the plates located thereon or even remove them when modern adhesives are used.
In order to overcome the problems inherent in the U.S. Pat. No. 3,146,709 wound printing sleeve, U.S. Pat. No. 3,978,254 has provided a mechanically adhered wound unitary printing sleeve in which three layers of adhesive tape are helically wound about a mandrel to form a carrier sleeve, with two of the helixes being wound at the same angle and the remaining helix being wound at a different angle. The convolution of the helixes are said to impart some degree of strength, rigidity and leakage protection to the printing sleeve. Furthermore, the outer surface of the U.S. Pat. No. 3,978,254 wound sleeve has a plurality of surface irregularities formed therein and is therefore not "round" to the extent required by the flexographic printing industry. These carrier sleeves are made of a flexible, thin tape material which provides a minimum of structural integrity which exhibit minimal strength and durability properties. Moreover, as the printing plates are adhered to the printing sleeves they may not be moved from one position to another as they are aligned on the sleeves surface. In order to trim material on the plate from the sleeve surface, they must be cut with a sharp instrument such as a knife. The synthetic plastic tape used to form the above-described sleeve cannot withstand even the minor cutting action required in positioning of the printing plates. Finally, with high speed printing presses of today, these sleeves can slip.
Dimensional stability is a problem in printing applications requiring that the outer surface of a printing sleeve structure have a true cylindrical shape. For example, in the flexographic printing industry, the outer printing surface must accurately conform to a uniformly constant, cylindrical outer shape in order to accurately imprint a print image onto a printing medium. Many of these prior art printing sleeves do not meet these requisite tolerance levels.
U.S. Pat. No. 2,287,122 is another type of printing sleeve which is made of a metallic material. As in the case of some wound sleeves, metallic sleeves are not readily expandable and therefore must have a wall thickness which is be quite thin, i.e., thicknesses of up to only about 0.005", in order to be capable of undergoing the limited expansion required in mounting printing sleeves. As indicated above, this minimum thickness level required of metallic sleeves is a problem in instance where thicker sleeves are required. Moreover, metallic printing sleeves are not durable and are susceptible to damage. For instance, kinks are easily formed in these sleeves during mounting, dismounting or storage operations.
U.S. Pat. Nos. 4,144,812, 4,144,813, UK 1,581,232, UK 2,031,801 and EPA 181,726 relate to non-cylindrical unitary printing sleeves and complementary associated air-assisted printing rolls designed in a tapered or stepped-transition configuration. In these systems, the change in the sleeve and printing roll diameter from one end to the other is progressive, i.e., increasing or decreasing according to the direction one is moving along the printing sleeve or roll. The printing roll comprises complementary outer surface to the above printing sleeve having a diameter at one longitudinal end greater than the other longitudinal end. The printing sleeve has an inner surface designed to form an interference fit with the outer surface of the printing roll only at the designated working position, and not along the entire axial uniform cross-sectional extent of the tapered sleeve. In this technology, the end user cannot employ its existing standard constant diameter cylinders, but must instead purchase new tapered print rollers and complementary tapered sleeves.
U.S. Pat. No. 4,903,597, which is owned by the common assignee of this patent application, is directed to a unitary, cylindrically-shaped printing sleeve axially mountable on and dismountable from a complementary cylindrically-shaped plate cylinder, and is incorporated herein by reference. This sleeve can be fabricated of a high strength material having a wall thickness of a least about 0.15 inches. Over a typical course of repeat circumferences for wide web flexographic printing use, i.e., 15-30 inch repeat circumference, plate cylinders would have 60 different circumferences at one-quarter inch intervals. When the print sleeves of U.S. Pat. No. 4,903,597 are employed in a similar application, the required number of plate cylinders are reduced by 50%. The remaining 50% of repeat circumferences are obtained by using the print sleeves whose cost is only a fraction of the cost of a plate cylinder.
In all the above printing sleeve applications air-assisted cylinders are required in order to mount or dismount printing sleeves. Typical or standard printing cylinders must be modified to be air-assisted. These air-assisted cylinders typically employ compressed air which may present safety problems. Prior to the use of sleeves, large inventories of premounted cylinders were maintained which is extremely costly. Additional expenses are incurred when standard cylinders are physically modified to accept internal air mounted sleeves. This modification to plate cylinders can be avoided when external air systems are employed. If external air-assisted structures are needed, one can use systems such as those set forth in U.S. Pat. No. 4,979,278 issued on Dec. 25, 1990, U.S. Pat. No. 5,046,231 issued Sep. 10, 1991, U.S. Pat. No. 5,062,193 issued Nov. 5, 1991, and U.S. Patent Application, Ser. No. 07/474,520 filed on Feb. 1, 1990, which are incorporated herein by reference, and invented by the inventor of this patent application and assigned to the assignee of this patent application, can be employed. In either case, these additional costs must be paid for by the end user and ultimately their customers.
Therefore, a need exists for a cylindrically-shaped sleeve which can be easily frictionally mounted onto or dismounted from conventional cylindrically-shaped cylinders, without incurring the cost of purchasing tapered print rollers or modifying present inventories of cylinders.